Electrical device



April 50, 1946.

E. C. WAHL BERG ELECTRICAL DEVICE 5 Sheets-Sheet 1 Filed Jan. 24, 1942 o@m R mm 3 QM, m. mo g *Q m6 3 3 w. 1 9mm April 30, 1946. E. c. WAHLBERGEI'JEC'I'RICAL DEVICE 5 Sheets-Sheet 2 INVENTOR.

Filed Jan. 24, 1942 April 30, 1946. E. c. WAHLBERG 2,399,25

ELECTRICAL DEVICE Filed Jan. 24, 1942 5 Sheets-Sheet 5 Hum April 30,1946. E. .C. WAHLBERG v fi ELECTRICAL DEVICE Fiied Jan. 24, 1942 5Sheets-Sheet 4 April 30, 1946. VE; QWAHLBERQ v2,399,272

ELECTRICAL DEVICE Filed Jan 24, 1942 5 Sheets-Sheet 5 Patented Apr. 30,1946 ELECTRICAL DEVICE Eric C. Wahlberg, Stamford, Conn., assignor toElectrolux Corporation, poration of Delaware New York, N. Y., a cor-Application January 24, 1942, Serial No. 428,018

22 Claims.

My invention relates to electric devices and more particularly toelectric motors of either alternating or direct current type.

One of the objects of my invention is to provide means for electricallybringing'the armature of an electric device into angular alignment witha, fixedpoint.

A further object of my invention is to provide, in combination withmeans for causing either direct or alternating current electric motorsto run in synchronism, means for bringing the armature shafts of theseveral motors into accurate mechanical or electrical angular alignmentbefore the motors are started to thereby assure that the motors will runin synchronism immediately upon starting. Thus, before the motors arestarted their shafts may be brought into alignment, and thereafter dueto the synchronous operation of the motors, this alignment may bemaintained during operation.

Another object of my invention is to provide an arrangement whereby aplurality of either direct current or alternating current motors may becaused to operate in synchronism, not only during the normal running ofthe motors, but.

also as they are slowing down to a stop.

. A still further object of my invention is to provide an improvedswitching means for use in connection with the above.

Further objects and advantages of my invention will be apparent from thefollowing description. considered in connection with the accompanyingdrawings which form a part of this specification and of which:

Fig. 1 is a wiring diagram illustrating one embodiment of my inventionas applied to direct current motors;

Fig. 2 is a wiring diagram illustrating a second embodiment of myinvention as applied to direct current motors;

'Fig. 3 is a wiring diagram illustrating a third embodiment of myinvention as applied to direct current motors;

Fig. 4 is a wiring diagram illustrating improved switching means;

Fig. 5 is a wiring diagram illustrating a further embodiment of myinvention as applied to synchronous motors; and

Fig. ,6 is a wiring diagram showing my invention as applied to aninduction motor.

Referring more particularly to Fig. 1, there is shown a plurality ofdirect current electric motors, designated generally by referencecharacter l0. Inasmuch as the three motors are identical, the samereference characters will be employed to designate corresponding parts.Each motor includes diametrically disposed poles l2 and I4 carryingfield windings l6 and I8, respectively. As shown, the windings l6 and I8in each motor are connected in series and the fields of the severalmotors are also connected in series and supplied with excitation currentfrom any suitable direct current supply 20.

Suitably mounted between the poles l2 and I4 is an armature including awindin 22 made up of a plurality of coils. Each coil is connected bymeans of a tap 24 with a segment of a commutator 26. Brushes 28 and 30are associated with the commutator and are located on the neutral plane,in the usual manner. The armature windings of the several motors areconnected through the brushes 28 and 36 in parallel by means ofconductors 32 and 34. These conductors are supplied with direct currentthrough a double-pole, double-throw switch 36.

As shown, this switch has iour poles-38, 46, 42 and 44, and a pair ofblades 46 and 48, poles 40 and 44 being connected together by means of aconductor 50. Direct current is supplied from any suitable source to theblades 46 and 48 by means of conductors 54 and 52 respectively.Conductor 32, which is connected to one brush 28 of each of the severalmotors, is also connected to the pole 44, while conductor 34 isconnected to pole 42. Consequently, when the switch is closed in theright hand position, current is supplied from the conductors 52 and 54through the switch to the conductors 32 and 34 and through them to thearmatures.

The armature of each motor carries three slip rings 56, 58 and'6ll, eachslip ring being connected to a different commutator bar or armature tapthrough taps 62, 64 and 66, respectively. It is not necessary that thetaps 62, 64 and 66 be equally distributed angularly around the armaturewinding, and in the wiring diagram the angular space between the taps 64and 66 is less than that between either of these and the taps 62.Associated with the slip rings 56, 58 and are brushes 68, 10 and 12,respectively. Corresponding brushes in the different motors areconnected together by means of conductors l4, l6 and 18, respectively.

A conductor 86 is connected to any one of the three conductors 14, 16 or18 and leads through a resistance 82 to the pole 38 of switch 36.

The above-described device operates as follows:

Assuming the switch 36 to be in open position, the motors will of coursebe at rest, inasmuch as no current is supplied to their armatures. If itis desired that the motors not only run in synchronism, but that theangular relationship of all the shafts be the same, the shafts areinitially angularly aligned by exciting the field windings I6 and I8 andby throwing the switch 36 to the left-hand position. This suppliescurrent from the line 54 through the blade 46 and conductor 8E3 to thebrush 12. From here it flows through the slip ring 60 and tap 6'5 to thearmature winding 22. Here the current divides and flows around thearmatures in both directions to the brush 28 and thence through theconductor 32 to the pole 44 and through conductor 50 to pole 4i) andthence through blade 48 to terminal 52, thus completing the circuit. Theabove-described how of current through the armature creates a magneticfield having a center line bisecting the angle between the brush 28 andthe tap 66. It will be,assumed that field pole i2 is a north pole andthe pole created in the armature between the brush 28 and the tap 66 isa south pole. Consequently, the armature will be turned in a clockwisedirection, inasmuch as the north field pole attracts the south armaturepole. As the rmature is turned in this manner, the angle between thebrush 28 and the tap 66 is increased and more of the armature windingsare included therebetween. This causes the center line of the magneticfield in the armature to shift clockwise so as to always bisect theangle between the brush 28 and the tap 62', and this continues untilthis center line coincides with the center line of the field poles. Thearmature is thus magnetically locked in this position. If the tap 66 isinitially on the opposite side of the center line of the field, thearmature will be turned counter clockwise until the center linescoincide.

The same thing occurs in the armature of all the motors and consequentlyall the shafts are brought into angular alignment.

The motors are now started by throwing the switch 36 to the right-handposition, whereupon direct current is supplied to the brushes 28 and 30through the conductors 32 and 34 and the armatures are caused to rotatein the usual manner. It is assumed that this rotation is in acounterclockwise direction.

As is well known, the voltage generated within the armature conductorsof a direct-current motor are alternatin current voltages. Consequently,three-phase alternating current flows through the taps 62, 64 and 66 tothe respective slip rings and thence through the brushes 68, Ti") and'12 to the conductors I4, 16 and T8. The frequency and voltage of thiscurrent depend upon the speed of the armature. In the event that thearmature of one of the motors tends to run slower than the otherarmatures, due for instance to an increased load, the frequency andvoltage of the current produced by that armature become less than thatproduced by the others. Current will thereupon fiow from the two othermotors, acting as generators with respect to the threephase circuit, tothe slower running motor and will bring that motor into synchronism withthe other two. In other words, the three-phase circuit causes the motorsto operate as synchronous machines, the machine which has a tendency torun slower acting as a synchronous motor and the others as generators.In this way, the three motors are caused to operate at exactly the samespeed, although that speed is not necessarily constant. Thus, anincrease in lead on ali of the motors will cause all of them to slowdown. Likewise, an increase in load on less than all of the motors wouldcause all of them to slow down a certain amount.

If it is desired to maintain the armature shafts of the several motorsin synchronism as they are stopped and to stop them in angularalignment, the switch 35 is again thrown to the left-hand position. Assoon as the blades 46 and 48 of the switch break contact with the poles42 and 44, respectively, the armature circuit is opened and the motorceases to produce torque. However, the inertia of the armatures wouldcause them to coast until brought to rest as a result of friction in thebearings and the resistance offered by the load. Inasmuch as the loadsand the friction acting on the diiierent motors may be different, theseveral armatures would be apt to coast different numbers ofrevolutions. While the three-phase circuit serves to hold the armaturesin synchronism at high speeds, after they have slowed down somewhat thecurrent generated at the lower speeds is not sufficient to hold them insynchronism if the resistance to rotation is different for the diiferentarmatures.

However, if the switch 36 is thrown to the lefthand position, directcurrent i caused to fiow through the tap B6 and the brush 28, aspreviously described. This produces a magnetic field in the rotatingarmature with the result that an alterna -ng current is generated in thestationary field windings. ihis current is short circuited through themachine supplying direct current to the terminals 2d and producesdynamic braking. At the same time an alternating current is generated inthe armature windings, due to rotation of the armature relative to theexcited field, and this current is short circuited through the machinesupplying direct current to the brush 28 and tap 6B, producing anadditional dynamic braking effect. Consequently, the armature is rapidlydecelerated, but this braking itself does not tend to stop the armatureat any particular angular position.

However, if it is assumed that the dynamic braking eifect stops thearmature with the tap 35 in the position shown in Fig. 1, a magneticfield is created in the armature having a center line midway between thebrush 28 and the tap with the south pole at this side of the armature.This south pole is attracted by the north field pole l2, and thearmature is turned clockwise until the center line of this field isaligned with the center line of the field coils, as previously described in connection with the initial positioning of the armature.Likewise, if the armature is stopped by dynamic braking in any otherposition it will be angularly positioned in the same manner as explainedfor initial positioning.

The same thing occurs in all of the motors. If during the decelerationthe resistance to rotation of one of the motors is greater than that ofthe others, which would tend to stop it after a lesser number ofrevolutions, the application of direct current to the tap 66 of eachmotor while the motors are still rotating in synchronism holds them insynchronous deceleration because, the alternating currents generated inthe field windings of the respective motors, previously described inconnection with the dynamic braking, are in phase as long as the motorsrotate at the same speed. However, if one motor starts to get out ofstep, the current generated in its field winding is out of phase withthat generated in the other field windings. This results in how ofcurrent from the faster motor to the slower one and the motors are inthis way brought back to synchronous speed.

Consequently, the armatures of the several motors rotate the same numberof revolutions dur ing the deceleration period and come to rest withtheir shafts in angular alignment.

In the embodiment of my invention illustrated in the wiring diagram ofFig. 2, there is shown another means for bringing the several armatureshafts into angular alignment either before the motors are started orafter they are stopped. The motors I are exactly the same as thoseillustrated in Fig. 1, and the three-phase circuit including theconductors I4, I6 and I8 is the same. However, two of these conductors,for instance conductors I6 and I8, are connected to the poles 02 and 90,respectively, of a double-pole, doublethrow switch 94. The blades 96 and98 of this switch are connected to a suitable D. C. supply I00. Theother tw poles I02 and I04 are connected to the conductors 32 and 34which supply current to the armature brushes 28 and 30.

The operation of the above-described device is as follows:

In order to align the armature shafts of the several motors, the switch94 is closed in the lefthand position. A direct current circuit is thusprovided through the conductor I8, brush I2, slip ring 60, tap 66, part221) of the armature winding 22, tap 64, slip ring 58, brush I0 andconductor I6. The current flowing through this circuit produces northand south poles in the armature. Inasmuch as the field coils of themotors are excited, the magnetic force rotates the armatures until thepart 22b of the armature coils is in alignment with the pole havingopposite polarity from that of section 22b, which is assumed to be poleI2. Thus, all of the armature shafts are brought into angular alignment.Due to the fact that, in this embodiment, the part 22b of the armatureWinding always contains the same number of turns, regardless of theangular position at which the armature may have come to rest, it is notnecessary to provide a resistance, such as that designated by referencecharacter 82 in Fig. 1, in order to avoid the possibility of a.short-circuit.

As soon as the armatures have been aligned, the switch 94 is thrown tothe right-hand position, whereupon current is supplied in the usualmanner to the armatures and the several motors develop torque and hencethe armatures are caused to rotate.

The three-phase circuit including the taps 62, 64 and 66, the slip rings56, 58 and 60, the brushes 68, I0 and I2 and the conductors I4, I6 andI0 cause the armatures of the motors to run in synchronism in exactlythe same manner as described above in Fig. 1, inasmuch as these circuitsin the two figures are the same.

When it is desired to stop the motors, the switch is again thrown to theleft-hand position,

with the result that two poles are produced in the armature, as abovedescribed, thus giving in effect a rotating magnet between the two fixedpoles. Consequently, the part 22b tends to stop in alignment with thepole I2. The braking effect thus produced in most cases would not besufficient to immediately bring the armature to rest, inasmuch asinertia would carry the part 22b past the pole I2, probably a pluralityof times. However, the dynamic braking effect as described in connectionwith Fig. 1, rapidly decelerates the motors until the attraction betweenthe field pole I2 and the pole in the armature between the taps '64 and66 is able to stop the armature in proper alignment. Duringdeceleration, the armatures of the various motors are held in step,chiefly as a result of the alternating currents generated in, andcirculating between the field windings of the respective motors.Consequently, all the armatures remain in synchronism until they arestopped, and all stop with the respective portions 22b in alignment withthe poles I2. Therefore, it is assured that the several armature shaftsmake exactly the same number of revolutions and stop in exact angularalignment.

The embodiment illustrated in Fig. 3 differs from that shown in Fig. 2only with respect to the manner in which the field coils of the severalmotors are connected. In Fig. 2 the fields of the different motors wereall connected in series, whereas in Fig. 3 the coils I6 and I8 of eachmotor may be in series or parallel, as is well known, and are shown inseries, but these coils are connected in parallel with the field coilsof the other motors. Excitation current is supplied to the conductorsI06 and I08, and the field coils of the different motors are connectedin parallel between these conductors.

This embodiment normally operates in exactly the same manner as doesthat shown in Fig. 2. However, it has the advantage that if the fieldcircuit of any one of the motors is inadvertently opened duringoperation, it would not result in depriving the other motors ofexcitation current. Consequently, a motor with the open field circuitwould stop, but the others would continue to operate, whereas in theembodiment illustrated in Figs. 1 and 2, an open field circuit in anyone motor would cause all of them to stop. For certain applications,however, this may be a desirable feature.

In any of these embodiments the supply of armature current to one of thearmatures could fail without stopping that motor. Under such conditionsthe other motors would operate as generators with respect to thethree-phase circuit and drive the first-mentioned motor in synchronismas a three-phase synchronous motor.

In the embodiment illustrated in Fig. 4, there is shown an improvedswitching arrangement for use in connection with the embodimentsillustrated in either Fig. 2 or 3., In Fig. 4, the constructions of themotors and connections therebetween are the same as shown in Fig. 2 andconsequently need not be described again.

Reference character IIO designates one tenninal of a field circuit towhich is connected a conductor IIZ. This conductor leads to one pole II4of a double-pole, single-throw magnetically operated switch, designatedgenerally by reference character II6. Switch II6 includes a plunger I IIwhich is urged upwardly by means of a compression spring H9. The plungeris provided with a button I2I by means of which it may be pushed downagainst the force of the spring, and with a holding coil I35 forretaining it in this position. A conductor H8 is connected to the poleI20 of this switch and leads to the field coil I 0. The field coils ofall the motors are connected in series and a conductor I22 leads fromthe field of the last motor in the circuit to the ground connection I24.

Reference character I26 designates one terminal of the armature circuitand is connected by means of a conductor I28 to the pole I30 of theswitch II6. Pole I32 is connected by means of a conductor I 34 to oneend of the holding coil I35 of switch H6. A conductor I31 connects theother end of coil I35 to one terminal of a magnetically operated switchI36. A conductor I38 connects the other terminal of switch I36 with ablade I40 of a double-pole, double-throw magnetically operated switchI42. This blade may make contact with either of the poles 44 or I45. Aconductor 54% leads from the ground connection I53 to the other bladeI52 of the switch I42. This blade may make contact with either the poleI54 or I56.

The blades I49 and IE2 are connected to a plunger I53 which is normallyheld in its uppermost position by means of the spring ISO, in whichposition the blades make contact with the poles I44 and IE4,respectively. A solenoid coil 162 is associated with the plunger 158 soas to draw the plunger downwardly against the force of the spring whenthe coil is energized. Any suitable quick return type of dashpot I59 isconnected to plunger 53 and acts to retard downward motion of theplunger under the influence of coil I82, while permitting quick upwardmotion under the influence of spring I30 when the coil is de-energized.One terminal of the coil is connected to the conductor I48, while theother terminal is connected by means of a conductor I64 with oneterminal of a push button type switch I65. The other terminal of thisswitch is connected by means of a conductor 56% with the conductor I34.

A conductor H is connected to pole I46 of switch I42 and leads to thebrushes 30 of the several motors, while a conductor I12 is connected tothe pole I53 and leads to the brushes 28 of the motors. A conductor I14is connected to the pole I44 and leads to the conductor 1B of thethree-phase circuit, while a conductor I15 connects pole I54 with theconductor 18 of this circult.

Switch I33 is provided with a solenoid coil I18 which is connected bymeans of conductors I80 and IE2 across the lines I14 and I16. Theplunger I151 of this switch is urged downwardly by means of a springI34, but this motion is retarded by a dashpot I8I.

The above-described device operates as follows:

When it is desired to start the motors the switch I55 is closed bypressing down button I2I. Consecuently, field current flows from theconductor I12 through the terminals H4 and I20 of the switch to theconductor H8 and thus through the field coils to the conductor I22 andthe ground connection I24.

Armature current flows from the conductor I28 through the terminals I31!and I32 of the switch I It to the conductor I34 and through the holdingcoil I35, to thereby energize the coil and thus hold the plunger I11down and the switch closed. From the holding coil the current flowsthrough switch I33, which is normally closed, to the blade I40 oi theswitch I42. From here the current flows from the terminal I44 throughthe conductor I14 to the conductor 13 of'the threephase circuit, andthence through the brush 18, slip ring 58, and tap 54 to the armaturewinding 22 where it divides and flows around parallel paths through thewinding 22 to the tap 66 connected to the slip ring 6! brush 12,conductors 13 and M6 to the terminal I54. From here the circuit iscompleted through the blade I52 and conductors I48 to the groundconnection I56. This causes the armatures of the several motors to beturned into angular alignment in the same manner as described in Fig. 2.

The closing of switch IIB also causes current to flow through theconductor I68, the normally closed switch I66 and the conductor I64 tothe solenoid I62 of the switch I42. The energizing of this solenoidtends to move the switch to its other position, but this action isdelayed by the dashpot I59 for a sumcient length of time to allow thearmatures to be turned into angular alignment. At the same time coil I13of switch I36 is energized and tends to open this switch. However, thisis delayed by the dashpot I8I, which is so selected as to be sloweracting than the dashpot I59 of switch I42. Therefore, the latter switchis shifted before switch I36 opens so that the blade I40 contacts theterminal I48 and the blade 152 contacts the terminal I55, thus supplyingarmature current through the conductors I10 and I12 to the brushes ofthe several motors, and cutting off the supply of current to conductorsI14 and I16 and hence tie-energizing coil I18. The motors now operate inthe normal manner and the three-phase circuit holds them in synchronism,as has been previously described.

When it is desired to stop the motors, the push button switch I65 isopened, thus de-energizing the holding coil I32. This permits the springISO to shift the switch I42 back to the position shown in Fig. 4.Consequently, direct current is supplied through the brushes !13 and I22and the motors are caused to stop in synchronism and in angularalignment.

Inasmuch as coil I13 is across lines I14 and 16, it is energized andopens the switch I33, the opening however being delayed by the dashpoti8i long enough for the armatures to be aligned. When switch opens, itopens the circuit through holding coil I35 and consequently spring H9moves plunger II1 upwardly to open switch II6.

While the motors illustrated in Figs. 1 through 4 have been described asbeing operated by direct current, they are shown as universal motors andhence will operate satisfactorily on either alternating or directcurrent. During positioning, if alternating current is employed, thepolarities of the field poles are reversed in accordance with thefrequency of the current, but at the same time the polarities of therelatively fixed poles established in the armatures are likewisereversed in the same manner and consequently, the armatures arepositioned relative to their fields when using A. C. in the same manneras described for D. C. operation.

Fig. 5 shows the application of my invention to a plurality ofthree-phase synchronous motors. Each motor includes a wound armature 230provided with slip rings 292, 204, 206 and 201 of which the first threeare connected through taps 208, 2H! and 2I2, respectively, to thearmature winding at points equally spaced around its circumference. Slipring 281 is connected to the winding through a tap 253 which is spacedfrom the tap 208 a distance less than the width of the pole faces.Brushes 2M, 2I6, H8 and 2I9 contact these slip rings and are connectedto conductors 220, 222, 224 and 225, respectively. These conductors areconnected to the blades of a fourpole, double-throw switch designatedgenerally by reference character 225. This switch is provided with a setof contacts 221, 228, 230 and 232 on one side and a similar set 235,236, 238 and 248 on the other side. The contacts 228, 230 and 232, whichmay be connected through the respective blades of the switch with theconductors 220, 222 and 224, are connected to the three-phase line 234,the contact 221 being dead.

2,399,272 I The contacts 235 and 236, which may be connected through theswitch to the conductors 225 and 220, are connected to a D. C. supplyline 242, the contacts 238 and 248 of this set being dead.

Each motor is provided with a plurality of field poles 244, the windings246 of which are connected in series and to a supply line 248 for directexcitation current, as is usual with a synchronous motor.

With the switch 226 in the left position, as viewed in Fig. 5,three-phase current is supplied from the line 234 to the conductors 220,222 and 224 and through the brushes 2l4, 216 and 218, the slip rings202, 264 and 286, and the taps 208, 2l6 and 212 to the armature winding260 of each motor. The field being excited by direct current from theline 248 the several motors will run in synchronism in the usual manner.

If it is-desired to stop the motors in synchronism and with therespective armatures in angular alignment, the switch 226 is thrown tothe right position. Consequently, the three-phase supply to the armatureis interrupted and direct current is supplied from the line 242 to theconductors 220 and 225, from where it passes through the brushes 2! and219, the slip rings 202 and 281 and the taps 288 and 213 to the armaturewinding. This establishes poles in the armature in the same manner asoccurs in the embodiment illustrated in Fig. 2. Inasmuch as the fieldcoils 246. are excited by direct current, they constitute Poles ofunchanging polarity, with the result that the armature of each machinewill be brought to rest with the north and south poles therein inalignment with the south and north poles, re spectively, of the field,In the same manner, as described in connection with Fig.2, the armaturesof the several motors are stopped in synchronism the rotor is turneduntil the north and south poles therein are in alignment with the southand north poles, respectively, established in the stator.

During operation of the motor the switch 294 is open and the switch 258is thrown to the righthand position, thus supplying three-phase currentto the stator, and the motor operates in the manner usual withthree-phase induction motors.

While I have shown and described several embodiments of my invention, itis to be understood that this has been done for purposes of illustrationOnly and the scope of m invention is not to be limited thereby, but isto be determined from the appended claims.

What I claim is:

1. In an electric motor, a stationar field, a rotatable armature,including an armature winding and a commutator, a pair of brushesassociated with said commutator for supplying current to said winding, aslip ring carried by said armature and connected to said winding, abrush associated with said slip ring, means for energizing said fieldwith direct current to thereby establish relatively fixed magneticpoles, and means for supplying direct current to one of the armaturebrushes and to the slip ring brush to thereby establish relatively fixedmagnetic poles in said armature.

and are accurately aligned angularly with respect to each other.

If desired, instead of providing the fourth connection 213 to thearmature, the direct current from the line 242 could be supplied to anytwo of the conductors 220, 222 and 224.

Fig. 6 illustrates how my invention may be utilized to angularly alignthe armature of an induction motor before starting, or after stopping,Reference character 250 designates a three-phase stator which may besupplied with current through the conductors conductors are connected tothe blades of a triplepole, double-throw switch 258, the poles 260, 262and 264 of which are connected to the threephase supply line 266. Anytwo of the other sets of poles 268, 210 and 212 are connected to adirect-current line 214.

The motor is provided with a wound rotor 216 having a pair of slip rings218 and 280 connected to spaced points of the rotor winding by means oftaps 282 and 284, respectively. Brushes 286 and 288 are associated withthe slip rings and are connected by means of conductors 298 and 282 withthe D. C, supply line 214, a double-pole, single-throw switch 294 beingprovided in the conductors 290 and 292.

In order to angularly position the rotor with respect to the stator, theswitch 294 is closed in order to supply direct current to the rotorwinding 216, to thereby establish poles therein. At the same time, theswitch 258 is thrown to the left-hand position, as viewed in thisfigure, whereupon direct current is supplied through the con ductors 254and 256 to the stator winding 25!). This serves to establish stationarypoles of unchanging polarity in the stator and consequently 252, 254and255. These 2. In an electrical system, a plurality of similar electricmotors, each motor including a stator and a wound rotor having acommutator, a plurality of conductors providing an alternating currentcircuit connected to similar points in the windings of the severalrotors, means for establishing relatively fixed magnetic poles inthe'several stators, means for connecting an electric circuit to saidseveral rotor windings to establish relatively fixed magnetic polestherein, one side of said electric circuit being connectable to saidwindings through one of said conductors, and means operativealternatively with said last mentioned means for supplying thecommutators of all of the motors with the same voltage.

3. In an electrical system, a plurality of similar electric motors, eachmotor including a stator and a wound rotor having a commutator, aplurality of conductors providing an alternating current circuitconnected to similar points in the windings of the several rotors, meansfor establishing relatively fixed magnetic poles in the several stators,means for connecting an electric circuit to said several rotor windingsthrough two of said conductors to establish relatively fixed magneticpoles in said rotors, and means operative alternativelywith said lastmentioned means for supplying the commutators of all of the motors withthe same voltage.

4. In an electrical system, a plurality of similar electric motors, eachmotor including a stator, a wound rotor, a commutator and a pair ofbrushes associated with said commutator, a plurality of conductorsproviding an alternating current circuit connected to similar points inthe windings of the several motors, means for establishing relativelyfixed magnetic poles in the several stators, and means for connecting adirect current circuit to said several rotor windings to establishrelatively fixed magnetic poles therein, one side of said direct currentcircuit being connected to said windings through one of said conductorsand the other side bein connected through one brush of each motor.

5. In an' electrical system, a plurality of similar electric motors,each motor including a stationary field, a wound rotor, a commutator, apair of brushes associated with said commutator, a plurality of sliprings connected to the rotor Winding at spaced points and a brushassociated with each slip ring, conductors connecting the slip ringbrushes of the several motors to provide an alternating current circuit,means for exciting said field with direct current, a double-pole,doublethrow switch, a source of direct current connected to said switch,and means for connecting the commutator brushes and two of said slipring brushes of each motor to said switch so that in one position of thelatter direct current is supplied to said rotor windings through thecommutators and in another position direct current is supplied to therotor windings through two of the slip rings.

6. In an electrical system, a plurality of similar electric motors, eachmotor including a stationary field, a wound rotor, a commutator, a pairof brushes associated with said commutator, a plurality of slip ringsconnected to the rotor winding at spaced points and a brush associatedwith each slip ring, conductors connecting the slip ring brushes of theseveral motors to provide an alternating current circuit, means forexciting said field with direct current, a double-pole, doublethrowswitch, a source of direct current connected to said switch, means forconnecting the commutator brushes and two of said slip ring crushes ofeach motor to said switch so that in one position of the latter directcurrent is supplied to the rotor windings of the several motors throughtwo of the slip rings and in another position is supplied to the rotorwindings through the commutators, and means for automatically shiftingsaid switch from the former to the latter position after it has occupiedthe former position a predetei mined period.

'7. In an electrical system, a plurality of similar electric motors,each motor including a stationary field, a wound rotor, a commutator, apair oi brushes associated with said commutator, a plurality of sliprings connected to the rotor winding at spaced points and a brushassociated with each slip ring, conductors connecting the slip ringbrushes of the several motors to provide an alternating current circuit,means for exciting said field with direct current, a double-pole,doublethrow switch, a source of direct current connected to said switch,means for connecting the commutator brushes and two of said slip ringbrushes of each motor to said switch so that in one position of thelatter direct current is supplied to the rotor windings of the severalmotors through two of the slip rings and in another position is suppliedto the rotor windings through the com.- mutators, a holding coilassociated with said switch and connected across said source of directcurrent for shifting said switch from the former to the latter positionand for holding the switch in the latter position, and means fordelaying the shifting of said switch for a predetermined period aftersaid coil has been energized.

3. In an electrical system, a plurality of similar electric motors, eachmotor including a stationary field, a wound rotor, a commutator, a pairof brushes associated with said commutator, a plurality of slip ringsconnected to the rotor winding at spaced points and a brush associatedwith each slip ring, conductors connecting the slip ring brushes of theseveral motors to provide an alternating current circuit, means forexciting said field with direct current, a double pole, doublethrowswitch, a source of direct current connected to said switch, means forconnecting the commutator brushes and two of said slip ring brushes ofeach motor to said switch so that in one position of the latter directcurrent is supplied to the rotor windings of the several motors throughtwo of the slip rings and in another position is supplied to the rotorwindings through the commutators, means for biasing said switch to theformer position, a holding coil connected across said source of directcurrent for shifting said switch from said former to the latter positionand for holding the switch in the latter position, means for delayingthe shifting of said switch for a predetermined period after said coilhas been energized, and a manually operable switch for deenergizing saidcoil.

9. In an electrical system, a plurality of similar electric motors, eachmotor including a stationary field, a wound rotor, at commutator, a pairof brushes associated with said commutator, a plurality of slip ringsconnected to the rotor winding at spaced points and a brush associatedwith each slip ring, conductors connecting the slip ring brushes of theseveral motors to provide an alternating current circuit, means forexciting said field with direct current, a double-pole, double-throwswitch, a source of direct current connected to said switch, means forconnecting the commutator brushes and two of said slip ring brushes ofeach motor to said switch so that in one position of the latter directcurrent is supplied to the rotor windings of the several motors throughtwo of the slip rings and in another position is supplied to the rotorwindings through 5 the commutators, means for biasing said switch to theformer position, a holding coil connected across said source of directcurrent for shifting said switch from said former to the latter positionand for holding the switch in the latter posi- 40 tion, a manuallyclosable switch in the circuit between said holding coil and saidsource, a holding coil connected in series in said circuit formaintaining the last-mentioned switch closed when current is flowing inthe circuit, means for delaying the shifting of said double-pole,doublethrow switch for a predetermined period after the first-mentionedholding coil has been energized, and a manually openable switch fordeenergizing said first-mentioned coil when said manually closableswitch is closed.

10. In an electrical system, a plurality of similar electric motors,each motor including a stationary field, a wound rotor, a commutator, apair of brushes associated with said commutator, a plurality of sliprings connected to the rotor winding at spaced points and a brushassociated with each slip ring, conductors connecting the slip ringbrushes of the several motors to provide an alternating current circuit,means for exciting said field with direct current, a double-pole,double-throw switch, a source of direct current connected to saidswitch, means for connecting the commutator brushes and two of said slipring brushes of each motor to said switch so that in one position of thelatter direct current is supplied to the rotor windings of the severalmotors through two of the slip rings and in another position is suppliedto the rotor windings through the commutators, means for biasing saidswitch to the former position, a holding coil connected across saidsource of direct current for shifting said switch from said former tothe latter position and for holding the switch in the latter position, amanually closable switch in the 011' cuit between said holding coil andsaid source,

a holding coil connected in series in said circuit for maintaining thelast-mentioned switch closed when current is flowing in the circuit,means for delaying the shifting of said double-pole, doublethrow switchfor a predetermined period after the first-mentioned holdin coil hasbeen energized, a normally closed switch in said circuit, a holding coilconnected across said two of said slip ring brushes for opening saidnormally closed switch, means for delaying the opening thereof for aperiod greater than said predetermined period, and a manually openableswitch for deenergizing said first-mentioned coil when said manuallyclosable switch is closed.

11. A plurality of rotary converters, means providing a three phaseconnection between the alternating current sides of said converters,means to appl direct current to the direct cur rent sides of saidconverters, and means operable on removal of the direct current fromsaid direct current sides of the converters to apply direct current toone phase of said three phase connection.

12. A plurality of direct current motors, means to position said motorsin the same relative phase angle position, means to accelerate saidmotors synchronously, means to maintain said motors in synchronism whilerunning, and means dynamically to brake said motors in synchronism.

13. A source of electric power, an electric motor, means to connect saidsource to the motor in such a manner as to cause the motor to operate,first switch means for controlling the lastmentioned means, electricmeans to position the motor in a desired position, means to connect saidsource to said electric means, second switch means for controlling thelast-mentioned means, electric means to brake the motor, means toconnect said source to the last-mentioned means, switch means forcontrolling the last-mentioned connecting means, and manual meansresponsive to a single movement by an operator for successivelyactuating said second switch means and said first switch means andresponsive to another single movement by an operator for successivelyactuating the first switch means and the switch means for controllingthe brake means and the second switch means.

14. A source of electric power, an electric motor, a first circuit forconnecting said source to the motor in such a manner as to cause themotor to operate, first switch means for controlling said circuit,electric means for positioning the motor in a desired position, a secondcircuit for connecting said source to said electric means,

second switch means for controlling said second circuit, electric meansfor dynamic braking of the motor, a dynamic braking circuit, switchmeans for controlling said braking circuit, and manual means responsiveto a single movement by an operator for successively actuating saidsecond switch means and said first switch means and responsive toanother single movement by an operator for first actuating the firstswitch means and then actuating the second switch means and the switchmeans for controlling said brakingcircuit.

15. A source of electric power, an electric motor, a first circuit forconnecting said source to the motor in such a manner as to cause themotor to operate, first switch means for controlling said circuit,electric means for positioning the motor in a desired position, a secondcircuit for connecting said source to said electric means, second switchmeans for controlling said second ill) means and responsive to anothersingle movement by an operator for successively actuating the firstswitch means and the second switch means.

16. In an electrical system, a plurality of electric motors having woundrotors, means for per-' manently electrically connecting like points inthe rotors of the several motors, means for establishing electricalconnections for positioning the rotating parts of the several motors inthe same relative angular positions before the motors are started, meansfor establishing other electrical connections for synchronouslyaccelerating said motors from rest to normal operating speed, saidlast-mentioned electrical connections also serving for running saidmotors in synchr n means for reestablishing the first-mentionedelectrical connections for synchronously decelerating said motors fromnormal operating speed to rest.

17. In an electrical system, a plurality of electrio motors having woundrotors, means for permanently electrically connecting like points in therotors of the several motors, means for establishing electricalconnections for supplying direct current to position the rotating partsof the several motors in the same relative angular positions withrespect to each other and in predetermined positions with respect to thestationary parts of the motors before the motors are started, means forestablishing other electrical connections for synchronously acceleratingsaid motors from rest to normal operating speed, said lastmentionedelectrical connections also serving for running said motors insynchronism, and means for reestablishing the first-mentioned electricalconnections for synchronously decelerating said motors from normaloperating speed to rest.

18. In an electrical system, a plurality of electric motors, electricmeans for positioning the rotating part of each motor in the sameangular position relative to the fixed part thereof as the rotatingparts of the remaining motors relative to their respective fixed partsbefore the motors are started, means to apply the same voltage to thedifferent motors to cause the motors to start and run, and meansproviding a path for the flow of synchronizing alternating currentsbetween the motors.

19. A plurality of direct current motors, means connecting like fixedpoints on the armature windings of said motors, direct current means forpositioning the armature of each motor in the same position with respectto its field as the armatures of the remaining motors relative to theirrespective fields, and means to apply the same voltage to each of themotors to cause them to start and run.

20. A plurality of electric motors, means connecting like fixed pointson the armature windings of said motors, means for applying electriccurrent to said first-mentioned means for positioning the armature ofeach motor relative to the field thereof in the same position as thearmatures of the remaining motors relative to their respective fieldsbefore they are started, and means to apply the same voltage to each ofthe motors to cause them to start and run.

21. In an electrical system, a plurality of electric motors, each motorincluding a stator and a wound rotor having a commutator, a plurality ofconductors providing an alternating current circuit connected to similarpoints in the windings of the several rotors, means for establishingrelatively fixed magnetic poles in the several stators, means forsupplying electric current, means for connecting said supply means totwo of said conductors to impress a potential on the several rotorwindings to establish relatively fixed magnetic poles in said rotors,and means operative alternatively with said last-mentioned means toconnect said supply means to said commutators to impress the samevoltage on each of the several rotor windings to create a rotatingmagnetic field therein.

22. A plurality of direct current motor each having a field winding andan armature winding, means interconnecting fixed taps taken from thearmature winding of each motor, a commutator for each armature winding,means to apply direct current electric power to the commutator of eachmotor, and means to apply direct current electric power to the meansinterconnecting the fixed taps when the means con necting thecommutators to direct current electric power have been disconnected butwhile the motors are still running to decelerate the motors insynchronisni and to stop them with the armature of each motor positionedrelative to the field thereof in the same position as the armatures ofthe remaining motor relative to their respective fields.

ERIC C. WAHLBERG.

